1. Field of the Invention
In general, this invention relates to hard disk drives having a multiplicity of sectors for storing data for operating-system and application programs. More particularly, it relates to such a drive having data-guarding firmware that controls an off-line scan to identify and repair marginal sectors.
2. Description of the Prior Art and Related Information
A huge market exists for magnetic hard disk drives for mass-market host computer systems such as servers, desktop computers, and laptop computers. To be competitive in this market, a drive must be relatively inexpensive, and must accordingly embody a design that is adapted for low-cost mass production. In addition, it must provide substantial capacity, rapid access to data, and reliable performance. Numerous manufacturers compete in this huge market and collectively conduct substantial research and development, at great annual cost, to design and develop innovative drives to meet increasingly demanding customer requirements.
These customer requirements include challenging specifications for performance (access time, data throughput, etc.) and capacity (contemporary capacity specifications are well in excess of 1 gigabyte per drive). These customer requirements also include exacting reliability and quality assurance standards which have as one of their purposes to ensure that a defect in the construction or operation of a drive does not cause loss of valuable data.
One general approach to reducing the risk of loss of data involves various ways to predict a forthcoming drive failure and providing a notice of the impending failure. An industry-sponsored committee has developed a relevant standard. This committee is referred to as the "Small Form Factor Committee." This standard is identified as the "Specification for S.M.A.R.T. SFF-8035 ver. 2.0." (S.M.A.R.T. is an acronym for Self-Monitoring, Analysis, And Reporting Technology.)
Another approach is disclosed in U.S. patent application titled "Verifying Write Operations in a Magnetic Disk Drive," Ser. No. 08/644,507, filed May 10, 1996, by Lawrence J. Barr and Anil Sareen, which is assigned to the same assignee as this application. The disclosure of this prior patent application is hereby incorporated by reference herein.
As for drives that provide for predicting an impending failure, such prior art drives can allow marginal sectors to cause adverse performance slowdowns with respect to reading data from the sectors. To provide reliability for marginal sectors, it is common to employ error correction techniques that involve multiple levels. One such level involves hardware-implemented techniques for forming "codewords"--usually Reed-Solomon codewords--that are written to the sectors, and for detecting and correcting errors on an "on-the-fly" basis (i. e., substantially simultaneously with the reading of the data from the sectors). Another such level involves firmware-controlled "heroic recovery" techniques. These firmware-controlled techniques include retries, elaborate calculations to correct burst errors that can not be corrected on the fly, and other techniques.
The execution of firmware-controlled heroic-recovery techniques can consume seconds of time, this being substantially more time than the time in the order of milliseconds normally involved in completing a read command. It is highly undesirable for an operating system or application program to wait repeatedly a few seconds each time heroic-recovery techniques are invoked.
As for drives that employ automatic verification operations as part of the overall write process, such prior art drives involve adverse performance slowdowns with respect to writing data to the sectors.
In summary of the foregoing, no prior art approach provides a comprehensive solution to meet dual goals of high reliability and fast performance--i.e., enhancing the reliability of accurate readout of data, without causing a slowdown affecting an operating-system or application program.